Although forest fires are a natural occurrence, recent fires are more extreme, and humans can take much of the blame. ‘‘Natural communities are adapted to routine fires,’’ says Scott Anderson, a professor of environmental sciences at Northern Arizona University in Flagstaff. ‘‘But the catastrophic fires that used to be uncommon are now occurring regularly. Instead of burning bark and needles, the fires are killing large, well-established trees.’’
...In a study published this year, Yale University paleoecologist Jennifer Marlon built a comprehensive fire record for the Western United States for the past 3,000 years. She found that hot, dry weather led to increased wildfires, while cold, wet weather suppressed fire. During the medieval warm period, for example, wildfires surged. Between 1500 and 1800, an era that researchers call the Little Ice Age, fires subsided. That intuitive relationship, which held up for nearly three millenniums, was severed more than 150 years ago.
...Americans embarked on a new era of active fire suppression: Railroads were required to clear trees within 100 feet of the track. The government built fire-lookout towers and cut fire roads through the forest. Eventually, modern machines, such as aircraft, were employed to put down fires wherever they sprang up.
...Although the 20th century was a relatively warm and dry period, Marlon’s study showed that until the end of the century approached, wildfire activity fell to around the levels last seen during the Little Ice Age. As a result, the Western United States now suffers from what Marlon calls a ‘‘fire deficit.’’ ‘‘A fire deficit is a gap between how much fire you would expect to have, given current levels of drought and temperature,’’ and the amount of fire that actually takes place, she explained.....
Fighting the Waldo Canyon Fire, shot by Charles McCain, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license
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